7,207 research outputs found
Hidden torsion, 3-manifolds, and homology cobordism
This paper continues our exploration of homology cobordism of 3-manifolds
using our recent results on Cheeger-Gromov rho-invariants associated to
amenable representations. We introduce a new type of torsion in 3-manifold
groups we call hidden torsion, and an algebraic approximation we call local
hidden torsion. We construct infinitely many hyperbolic 3-manifolds which have
local hidden torsion in the transfinite lower central subgroup. By realizing
Cheeger-Gromov invariants over amenable groups, we show that our hyperbolic
3-manifolds are not pairwise homology cobordant, yet remain indistinguishable
by any prior known homology cobordism invariants. Additionally we give an
answer to a question about transfinite lower central series of homology
cobordant 3-manifold groups, asked by T. D. Cochran and M. H. Freedman.Comment: 24 pages; a new theorem answering a question of Cochran and Freedman
(Kirby List 3.78) added; referee's comments incorporated; to appear in J.
Topolog
Weak ties: Subtle role of information diffusion in online social networks
As a social media, online social networks play a vital role in the social
information diffusion. However, due to its unique complexity, the mechanism of
the diffusion in online social networks is different from the ones in other
types of networks and remains unclear to us. Meanwhile, few works have been
done to reveal the coupled dynamics of both the structure and the diffusion of
online social networks. To this end, in this paper, we propose a model to
investigate how the structure is coupled with the diffusion in online social
networks from the view of weak ties. Through numerical experiments on
large-scale online social networks, we find that in contrast to some previous
research results, selecting weak ties preferentially to republish cannot make
the information diffuse quickly, while random selection can achieve this goal.
However, when we remove the weak ties gradually, the coverage of the
information will drop sharply even in the case of random selection. We also
give a reasonable explanation for this by extra analysis and experiments.
Finally, we conclude that weak ties play a subtle role in the information
diffusion in online social networks. On one hand, they act as bridges to
connect isolated local communities together and break through the local
trapping of the information. On the other hand, selecting them as preferential
paths to republish cannot help the information spread further in the network.
As a result, weak ties might be of use in the control of the virus spread and
the private information diffusion in real-world applications.Comment: Final version published in PR
A Concise Total Synthesis of (--)-Maoecrystal Z
The first total synthesis of (--)-maoecrystal Z
is described. The key steps of the synthesis include a
diastereoselective Ti^(III)-mediated reductive epoxide coupling reaction and a diastereoselective Sm^(II)-mediated reductive cascade cyclization reaction. These transformations enabled the preparation of (--)-maoecrystal Z in only 12 steps from (--)-γ-cyclogeraniol
Prioritising project management competences across the software project life cycle
Purpose
The purpose of this paper is to investigate the relative importance of project management (PM) competences across the different stages of a software project life cycle to identify competence development gaps and opportunities.
Design/methodology/approach
A deductive and quantitative approach was adopted to address the research questions with a web-based survey for data collection.
Findings
After reviewing the context of competences and PM competences, the importance of the PM competences overall and for specific stages in the project life cycle was analysed. The result highlights that functional and meta-competences are perceived to be the most important competence dimensions for software project practitioners.
Originality/value
This study makes three contributions. First, it consolidates PM competences into a set of 20 within four competence dimensions. Second, it prioritises these competences across the software project life cycle. Third, it identifies the significance of the inter-relationship between PM competences and project life cycle to reveal PM competence development gaps and opportunities
Origin of Excitation Energy Dependence on Valence Nucleon Numbers
It has been shown recently that a simple formula in terms of the valence
nucleon numbers and the mass number can describe the essential trends of
excitation energies of the first states in even-even nuclei. By
evaluating the first order energy shift due to the zero-range residual
interaction, we find that the factor which reflects the effective particle
number participating in the interaction from the Fermi orbit governs the main
dependence of the first excitation energy on the valence nucleon numbers.Comment: 9 pages, 5 figure
Does rationality matter to the central bank?
Rationality is one of the main assumptions in economics, and is
represented as the rational expectation in macroeconomics. As
such, it is important to note that the effectiveness of economic
policy depends on the degree of economic agents’ rationality.
According to this point of view, it is only natural to ask how the
central bank views economic agents to be either rational or
bounded rational. In implementing economic policies, it is possible to assume that the central bank views economic agents to
be bounded rational. This is due to the fact that most theoretical
arguments state that policy under rationality is not as effective as
one under bounded rationality. Based on this argument, this
paper employs bounded rational New Keynesian Model proposed
by Gabaix to know if rationality matters to the central bank. As a
result, as long as the central bank does not follow the full gradualism, it is possible to conclude that the rationality matters to
the central bank. However, it is not anymore if the central bank
employs full gradualism in monetary policy rule
Costimulatory Molecules in Rheumatic Diseases Revisited with an Emphasis on Their Roles in Autoimmune Sjögren’s Syndrome
Superfluid-insulator transition of the Josephson junction array model with commensurate frustration
We have studied the rationally frustrated Josephson-junction array model in
the square lattice through Monte Carlo simulations of D XY-model. For
frustration , the model at zero temperature shows a continuous
superfluid-insulator transition. From the measurement of the correlation
function and the superfluid stiffness, we obtain the dynamical critical
exponent and the correlation length critical exponent . While the dynamical critical exponent is the same as that for cases
, 1/2, and 1/3, the correlation length critical exponent is surprisingly
quite different. When , we have the nature of a first-order transition.Comment: RevTex 4, to appear in PR
Localized ferromagnetic resonance force microscopy in permalloy-cobalt films
We report Ferromagnetic Resonance Force Microscopy (FMRFM) experiments on a
justaposed continuous films of permalloy and cobalt. Our studies demonstrate
the capability of FMRFM to perform local spectroscopy of different
ferromagnetic materials. Theoretical analysis of the uniform resonance mode
near the edge of the film agrees quantitatively with experimental data. Our
experiments demonstrate the micron scale lateral resolution in determining
local magnetic properties in continuous ferromagnetic samples.Comment: 7 pages, 3 figure
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